Local optical density of states in SiO2 spherical microcavities: Theory and experiment - art. no. 033807

The local optical density of states (LDOS) in 340-nm-diam SiO2 spherical mi crocavities was calculated and probed experimentally by measuring the lumin escence decay rate at 1.54 mum of erbium ions implanted in the colloids. To separate the effect of nonradiative processes, first the radiative decay r ate of Er3+ in bulk SiO2 was determined. This was done by varying the LDOS in an Er-doped planar SiO2 film by bringing the film into contact with liqu ids of different refractive index in the range n = 1.33-1.57. By comparing the calculated LDOS with the observed changes in decay rate with index, the radiative rate was found to be 54+/-10 s(-1) (tau = 18+/-3 ms) in bulk SiO 2. This value was then used to analyze the difference in decay rate in coll oids surrounded by air or immersed in an index-matching Liquid. Within the experimental error, agreement was found between the calculated and experime ntally probed LDOS in the colloids. Finally, a full determination of the LD OS vs size in SiO2 microcavities is presented (2 piR/lambda = 0.1-6.9), whi ch shows the appearance of a number of maxima, corresponding to the positio n of the electric-type resonances inside the microcavity.